SHUTOFF AS 4788195 - Caterpillar

Illustration 1 g00677004
PMPE Generator Wiring Diagram
(CR1-CR6) Diodes
(CR7) Varistor
(L1) Exciter field (stator)
(L2) Exciter armature (rotor)
(L3) Main field (rotor)
(L4) Main armature (stator)
(L5) Pilot exciter armature
(PM) Permanent magnet
(RFA) Rotating field assembly
(CST) Customer supplied transformer Ohmmeter
An ohmmeter can be used to check a varistor (CR7). Place an ohmmeter across the varistor. The resistance should be a minimum of 15000 ohms. If the resistance is less than 15000 ohms, the varistor is faulty.Test Light
Illustration 2 g00555113
Test Light
Refer to the test light that is shown in Illustration 2. Follow these steps in order to test the varistor:
Disconnect either lead of the varistor (CR7).
Place the test light across the varistor.
Observe the results. The lamp should not light.
Reverse the test light.
Observe the results. The lamp should not light. If the test light illuminates in either direction, there is a short in the varistor. Replace any faulty varistors with varistors that have comparable operating characteristics. Include the following information when a varistor is being ordered for replacement:
Part number of the varistor
Serial number of the generatorAfter the varistor has been replaced, verify that the strapping of the field winding lead is securely wound on the shaft. Also, verify that the strapping of the field winding lead is securely tied.